Torque motor-driven spool valves are well known in the art including such valves which operate through the utilization of a rotary torque motor having a drive member extending from the rotor thereof into contact with the spool valve to directly reciprocate the spool valve within a bore provided in the valve housing to thereby control the flow of fluid from a source thereof to the load in response to electrical signals applied to the drive motor. Typical of such direct drive servovalves is that illustrated in U.S. Pat. No. 4,793,377 issued Dec. 27, 1988, to Larry E. Haynes et al. The invention described and claimed herein is an improvement over the direct drive servovalve disclosed in U.S. Pat. No. 4,793,377 and therefore the disclosure of U.S. Pat. No. 4,793,377 is incorporated herein by this reference.
Other prior art known to applicants are U.S. Pat. Nos. 1,319,953; 2,264,635; 2,516,567; 3,762,784; 3,809,363; 4,249,782; 4,340,262; 4,408,808 and 4,772,136.
It is desirable in direct drive servovalves that the rotor of the drive motor be immersed in fluid for lubrication, heat transfer and pressure equalization. In prior-art valves, it has been traditional to allow the system fluid to freely flow into the rotor section of the motor. In such instances if the fluid is, or becomes, contaminated, foreign particles may become lodged in the rotor and degrade operation of the drive motor. Attempts to resolve this problem have resulted in the use of filters or seals to preclude passage of contaminants, however, such devices also limit the ability of the fluid to properly lubricate or transfer unwanted heat.